1. Field of the Invention
The present invention relates to a toner for electrophotography, used for developing an electrostatic latent image in electrophotography, static recording, etc.
2. Related Background Art
In processes for forming images by the use of electrophotographic systems, an electrostatic latent image is formed on an inorganic photoconductor comprised of selenium, a selenium alloy, cadmium sulfide, amorphorous silicon or the like or an organic photoconductor making use of a charge-generating material and a charge-transporting material, which is then developed using a toner, and transferred to a sheet such as paper or plastic film, followed by fixing to obtain a visible image. The photosensitive member can be constituted to have either a positive chargeability or a negative chargeability. In the case when print areas are left as an electrostatic latent image as a result of exposure, development is carried out using an opposite-sign chargeable toner. On the other hand, in the case when print areas are charge-eliminated to effect reversal development, the development is carried out using a same-sign chargeable toner. Toners are comprises of a binder resin, a colorant and other additives, where a charge control agent is commonly used so that desired triboelectric characteristics such as charge up speed, charge level and charge stability or storage stability and environmental stability can be imparted to the toners. This charge control agent greatly influences the characteristics of toners. Negatively chargeable toners are used in the case when development is carried out using the opposite-sign chargeable toner by the use of a positively chargeable photosensitive member and also in the case when reversal development is carried out by the use of a negatively chargeable photoconductor, and negative charge control agents are used in such cases.
In the case of color toners, it is necessary to use pale, preferably colorless, charge control agents that do not adversely affect hues. Such pale, or colorless, charge control agents include, for example, metal complex compounds of hydroxybenzoic acid derivatives as disclosed in Japanese Patent Publication No. 55-42752Japanese Patent Application Laid-open No. 61-69073 and No. 61-221756, etc.; metal aromatic dicarboxylate compounds as disclosed in Japanese Patent Application Laid-open No. 57-111541; metal complex compounds of anthranilic acid derivatives as disclosed in Japanese Patent Application Laid-open No. 61-141453, No. 62-94856, etc.; organic boron compounds as disclosed in U.S. Pat. No. 4,767,688, Japanese Patent Application Laid-open No. 1-306861, etc.; and biphenol compounds as disclosed in Japanese Patent Application Laid-open No. 61-3149. These charge control agents, however, have disadvantages such that they are chromium compounds having a possibility of environmental pollution, they are materials that can not be perfectly colorless, or they have a low charge-providing effect, give inversely charged toners and have a poor dispersibility or stability. Thus, none of conventional charge control agents have a satisfactory performance.